PhD, Professor of Aerospace Engineering, Department Chair,
Director of the Active Aeroelasticity and Structures Research Laboratory,
College of Engineering, University of Michigan, USA
https://scholar.google.com/citations?user=llBGc_0AAAAJ

 

Load alleviation for very flexible aircraft

Transport aircraft designs are evolving towards having wings with higher aspect ratio to improve aerodynamic performance and meet demanding flight mission specifications for reduced fuel consumption, lower emissions, and more efficient flight. With the resulting increased wing structural flexibility, flight loads also increase. Airworthiness certification mandated by regulatory agencies requires demonstrating that critical loads in these aircraft do not exceed specified limits that ensure safety and structural integrity. Active load alleviation schemes can enable reduced structural mass while satisfying certification requirements. Conventional approaches to maneuver load alleviation call for automatically deflecting control surfaces, such as elevons, to concentrate lift inboard and reduce the wing bending moment at critical stations. These control surfaces are deflected proportionally to some monitored parameters (e.g., load factor or wing curvature), which are obtained from sensor measurements. This presentation will address the challenges encountered on load alleviation for very flexible aircraft (VFA). It will start by reviewing the unique aeroservoelastic challenges that arise from large deformations of the wings and coupled aeroelastics—flight mechanics behavior, and the importance of having a framework able to capture geometrically nonlinearities to allow the study of how the loads (and vibration) characteristics changes when compared with a more traditional, less flexible aircraft. This will be followed by a proposed control technique to enable maneuver load alleviation (MLA) based on reference governor and model predictive control. Based on these numerical studies, a half-aircraft model of a VFA is studied in the wind tunnel. The experimental results confirmed the ability of the control technique to reduce loads but also indicated remaining challenges to be address for such solution. The presentation will end with a short outlook on how we intend to extend the MLA to also address gust load alleviation (GLA) and how to bring those load alleviation concepts into the multidisciplinary aircraft design.

Dr.Ir., Professor of Applied Mechanics,
Munich Institute for Robotics and Machine Intelligence,
Faculty of Mechanical Engineering, Technical University of Munich, Germany
https://scholar.google.com/citations?user=t74Xn_IAAAAJ

 

Experimental substructuring: an efficient strategy in noise and vibration analysis

When numerical structural models are highly complex, it is common to decompose them into several subdomains, treat those subdomains separately for instance by reducing them to their essential dynamics (model reduction), then re-assembling them to construct an accurate complete model that can be solved with little effort. This idea of substructuring, known for many years in dynamic simulations, can also be applied when components are characterized by their measured dynamics (e.g Frequency Response Functions). Including experimental substructure in a global model of a complex structure has several advantages, especially in the initial phase of development of new products when no numerical models of components exist, or when troubleshooting noise and vibration problems at a later development stage. Thanks to the availability of cheap and accurate sensors and acquisition systems, but also to new mathematical formulations of the assembling process, techniques such as the Frequency-Based Substructuring and Blocked Force approaches have become popular also in industry. We will explain the fundamental ideas behind those techniques and discuss several important practical tricks and best practices that are essential to make an experimental substructuring analysis successful. We will also indicate how those approaches can be used to characterize the dynamics of joints. Finally, we will discuss time-based substructuring strategies that are currently developed to analyze shock problems.

PhD, Professor of Aerospace Structures,
Laboratory for the Design of Reconfigurable Metamaterials and Structures,
Department of Civil, Environmental and Mechanical Engineering, University of Trento, Italy
https://scholar.google.com/citations?user=0xxJCXoAAAAJ

 

Cloaking, vibration suppression, and energy harvesting in metastructures

Leveraging recent advancements in cloaking technology and nonlinear resonators, we introduce a cloaked metastructure that integrates compact nonlinear magneto-piezoelectric oscillators. This design enables efficient vibration attenuation and energy harvesting across a broad frequency range, ensuring long-term structural health and operational functionality while optimizing performance. The core of the system is a meta-beam equipped with uniform voids that house nonlinear piezoelectric beams, which actively reduce vibrations and facilitate energy harvesting. A cloaking strategy, based on the reinforcement of the boundary and mass redistribution, is applied to strategically surround the voids, maintaining the same modal properties as a continuous beam. This cloaking design preserves structural integrity, tunability, and optimizes system performance. Theoretical and numerical analyses have been complemented by non-standard vibration experiments, validating the predicted outcomes. These results pave the way for the development of highly efficient and reliable energy harvesting systems, offering significant potential for future applications in vibration control and energy management.

Dr. Techn., Professor,
Head of the Microtechnology Research Center,
Vorarlberg University of Applied Sciences, Austria
https://scholar.google.com/citations?user=CSZQu7QAAAAJ

 

Exploiting energy transfer by time-periodicity in transient dynamics

Time-periodicity introduced in one or more system parameters is commonly associated with the risk of parametric resonance. However, when properly designed, time-periodicity becomes a key to achieving a controlled energy transfer between vibrational modes. Inducing such an energy transfer between a lightly damped and a highly damped vibration mode is capable of increasing the effective damping of the underlying system with constant coefficients. Subsequently, this leads to a faster decay of vibration or to a stabilization of an originally unstable system. At such a specific and beneficial time-periodicity, the system
operates in a state of a so-called parametric anti-resonance. This concept is applicable for systems with at least two degrees of freedom. It has been studied theoretically and validated in various experiments ranging from macroscopic engineering structures like beams and rotors to microscopic sensors realized as MEMS. Starting with analytical tools for the analysis of time-periodic systems, conditions for a successful design of this concept are derived and a theoretical performance measure is defined. An outlook is given to potential applications of parametric anti-resonance. In rotordynamics, this concept has the capability of achieving low-speed balancing of high-speed modal unbalance. In electromechanical energy harvesting, the low frequency vibrations can be shift to high frequency by modal energy transfer. In MEMS, the latency of a lightly damped sensor can be greatly reduced by a multi-harmonic or cascaded parametric anti-resonance. Several experimental validations across various mechatronic systems are discussed and the most successful implementations are highlighted.

PhD, Professor of Aerospace Engineering,
Director of the Space Structures and Systems Laboratory,
Department of Aerospace and Mechanical Engineering, University of Liège, Belgium
https://scholar.google.com/citations?user=a-qJ-JEAAAAJ

 

Experimental continuation: a paradigm shift in nonlinear dynamics

Nonlinear vibration theory witnessed extraordinary advances during the 20th century following Poincaré’s seminal work. Since the 1970s, impressive progress has been made in computational nonlinear dynamics with the development of nonlinear finite element methods and numerical continuation. Although not all challenges have been overcome yet, the theoretical understanding of nonlinear dynamical phenomena and their prediction using numerical models have reached a high level of maturity. Surprisingly, this progress has not significantly impacted engineering practice. Specifically, vibration testing in industry remains grounded in the assumption of linearity. To fill the existing gap, a vibration testing strategy which can uncover the sometimes dangerous, sometimes beneficial nonlinear dynamics of engineering structures is needed. In this context, experimental continuation leverages feedback control to identify experimentally – in a model-free and real-time manner – the bifurcation diagram of a nonlinear system. This presentation will review the state of the art in the area of experimental continuation and will introduce a new method, termed arclength control-based continuation (ACBC). This method will be illustrated using numerical and experimental examples.